1. Field of the Invention
This invention relates to a cyanoacrylate adhesive containing 2-cyanopentadienoic acid ester and to its production and use.
2. Discussion of Related Art
Cyanoacrylate adhesives are one-component reactive adhesives based on monomeric 2-cyanoacrylates. They have cornered the market through extremely quick curing which, depending on the substrate, takes only a few seconds. The resulting properties satisfy many industrial requirements. However, there are special applications where they are still in need of improvement. For example depolymerization is possible at temperatures of only around 100.degree. C. so that prolonged exposure to temperatures above 80.degree. C., should be avoided.
This problem of inadequate heat stability has been repeatedly discussed, for example in Journal of Applied Polymer Science 49, (1993), pages 1387-1394. This literature reference first of all describes the production and characterization of alkyl-2-cyano-2,4-pentadienoates and alkyl-2-cyano-2,4-hexadienoates and of bis-(2-cyano-2,4-hexadienoates) and then investigates the effect of adding 10% by weight of individual alkyl esters on the thermal stability of polycyanoacrylic acid propyl ester. The results show that heating for 1 hour to 150.degree. C. does not have an adverse effect on strength at 25.degree. C. In the absence of such an addition, however, there is a reduction in strength to about one quarter of the original value. There is no reference to strength at elevated temperature, nor any indication of how it can be improved.
WO 94/15907 describes cyanoacrylate adhesives with improved resistance to heat and moisture through the use of cyanoacrylate-terminated linear polymers, for example polyisobutylene or polyalkyl methacrylates (see page 4, line 16 to page 5, line 7 and page 10, line 27 to page 11, line 12). There are no specific references either to the composition of the adhesives or to their adhesive properties.
The fact that an addition of biscyanoacrylates to cyanoacrylate adhesives can lead to problems, particularly in regard to storage life and curing rate, is well known. In Journal of Polymer Science: Polymer Chemistry Edition, Vol. 16, pages 2475-2507 (1978), Carl J. Buck describes a mixture of isobutyl cyanoacrylate and bis-(2-cyanoacrylates). N,N-dimethyl-p-toluidine (DMPT) is required to initiate the polymerization reaction. A composition of 90% by weight of methyl cyanoacrylate and 10% by weight of octanediol bis-cyanoacrylate takes one day to cure at 38.degree. C. (see page 2504, last paragraph, and page 2505).
Against the background of this prior art, the problem addressed by the present invention was to provide a cyanoacrylate adhesive which would show increased heat resistance for substantially the same storage behavior and acceptable cure times.